Residual Stress in Siliceous Glass Between Mullite Crystals

A birefringence of siliceous glass, which is coexisting with mullite crystals, was studied by an optical polarizing microscope. The cause of the birefringence was assumed to be the residual stress induced by a large contraction difference between the mullite and glass on cooling. The stress has been evaluated to be as high as—0.3 GPa, and to correspond to the elastic one which began to develop at the glass transition point.     

Short- and long-term strength characteristics of particulate-filled cast epoxy resin

Particulate-filled thermosetting composites are widely used, yet little systematic work has been done on their long-term strength characteristics. In this study short-term tensile, flexural, and impact tests as well as tensile creep-rupture tests were made for unfilled and filled epoxy to clarify the effects of filler size, filler content, and temperature. Fillers used were silica, alumina particles, and glass beads. Test temperatures were varied from 25 to 110°C. As a result of short-term testing, it was found that the Petch relation held between strength and filler size if brittle fracture occurred, while a strength and filler size if brittle fracture occurred, while a strengthening effect existed when ductile fracture occurred. On creeprupture testing, a strengthening is observed with filler size and content for silica and glass beads. The Arrhenius plot of rupture time for various filler sizes and contents converges to a characteristic point corresponding to the glass transition temperature of the material. Using this relation, a modified Larson-Miller master rupture curve is proposed which can predict the long-term strength of particulate-filled thermosetting composites as functions of rupture time, temperature, filler size, and content.     

Composition of Corn Hull Dietary Fiber

The corn hull dietary fiber was decomposed into their components such as cellulose, hemicellulose-A, -B, -C, -other and lignin by the Siegel method, and their contents were 16%, 1%, 57%, 14% and 2%, respectivity. The components of ordinary corn fiber were insoluble in water, but several decomposed fractions were able to dissolved. The solubility in water of hemicellulose-B was well and of hemicellulose A was slightly, but other fractions were insoluble. Hemicellulose-A, -B, -C and -other fractions were made up of about 30% of arabinose and 50% of xylose. Uronic acid contents and solubility in water of each hemicellulose fraction were mutually related.     

Development of non-contact SIBIE procedure for identifying ungrouted tendon duct

For non-destructive evaluation (NDE) of concrete structures, the impact-echo method has been successfully applied to locate defects and voids in concrete. To compensate the difficulty in selecting the resonant frequency and to visually locate a defect, an imaging procedure named stack imaging of spectral amplitude based on impact-echo (SIBIE) has been developed. Combining the SIBIE analysis with the detection by a laser vibrometer, a non-contact procedure is studied to develop an automated system.Since waveforms detected by the laser vibrometer are undistorted, elastic waves generated due to a steel-ball drop were investigated theoretically as Lamb's problem in elastodynamics. It is confirmed that the first motion of detected waves by the impact-echo method is identical to Lamb's solution for a surface pulse, when reflected waves arrive later than the Rayleigh wave.An applicability of a non-contact SIBIE procedure to identify an ungrouted tendon duct of plastic sheath was examined in the impact-echo tests, as well as the duct of metal sheath. In order to study theoretically the SIBIE procedure for identifying ungrouted tendon ducts, the three-dimensional boundary element method (3D-BEM) was applied to synthesize frequency spectra. It is confirmed that frequency spectra detected in the tests are in good agreement with those synthesized. An applicability of the SIBIE procedure is also confirmed by the synthesized spectra. Results of the experiments show that the presence of the ungrouted duct can be visually identified by the non-contact SIBIE procedure in both the cases of plastic sheath and metal sheath.     

Doping effect on sinterability of polycrystalline yttria: From the viewpoint of cation diffusivity

The sintering behavior of Y₂O₃ doped with 1 mol% of a trivalent or tetravalent cation was investigated by pressureless sintering in air. Ga³⁺ or Ge⁴⁺-doped Y₂O₃ bodies exhibited higher relative densities than the undoped Y₂O₃, while the La³⁺ or Zr⁴⁺-doping suppressed the densification of Y₂O₃. An interdiffusion experiment was performed on the diffusion couples of polycrystalline Er₂O₃ and Y₂O₃ doped with Ni²⁺ or Zr⁴⁺, which are some of the most effective and least effective dopants for the improvement of the sinterability, respectively. The lattice and grain boundary diffusion coefficients of the Er³⁺ cation in Y₂O₃ were increased by the Ni²⁺-doping, but were decreased by the Zr⁴⁺-doping. High-resolution transmission electron microscopy observations and nano-probe X-ray energy dispersive spectroscopy analyses confirmed that the dopant cations segregate along the grain boundaries without forming an amorphous phase. The doping effect on the sinterability of Y₂O₃ must result from the change in the diffusivity in Y₂O₃.     

Hydrogen production by combining two types of photosynthetic bacteria with different characteristics

The double-layer photobioreactor using two types of photosynthetic bacteria, Rhodobacter sphaeroides RV and its reduced-pigment mutant, MTP4, was developed for efficient hydrogen production. The two types of bacteria had different characteristics on light energy, hydrogen production rate and conversion efficiency. MTP4 produced hydrogen more efficiently under high light conditions and RV did so under low light conditions. Illuminated light toward the surface of a photobioreactor quasi-exponentially declines as it penetrates into the reactor. When two types of bacteria were placed using the developed reactor according to this light distribution, the hydrogen production rate reached 3.64 l/m²/h at a light intensity of 500 W/m² in 24 h and the conversion efficiency of light energy to hydrogen was 2.18%. These values were 33% higher than those of only using RV. The low light in the deep part of the reactor was utilized efficiently, resulting in a higher hydrogen production rate.     

Novel Fabrication of High-Quality ZrO2 Ceramic Thin Films from Aqueous Solution

We report on the direct deposition of high-quality ZrO₂ thin films on various kinds of substrates by the liquid phase deposition method. After reaction for 24 h, thin films formed on various kinds of substrates, and the obtained thin film was comprised of densely packed nano-sized particles. The film annealed at 500°C showed a tetragonal phase at room temperature and this phenomenon has been discussed from the viewpoint of crystallite size effect. The result of optical transmittance measurement revealed that high transparency, more than 70% transmittance, has been achieved for the film after annealing at 900°C.     

Ultra micro glutamate sensor using platinized carbon-fiber electrode and integrated counter electrode

An integrated ultra micro glutamate sensor has been constructed with a 7 μm diameter platinized carbon-fiber disk (PCD) electrode and a platinum thin-film (PTF) counter electrode fabricated on the glass capillary tube. By platinization, the electrode activity of the carbon fiber is improved. In order to obtain a stable response, a pulse potential is applied for hydrogen peroxide measurement. The PTF counter electrode shows good stability and can be used as a substitute for a silver-silver chloride electrode. Since the integrated PCD electrode shows good characteristics as a hydrogen peroxide sensor, glutamate oxidase is immobilized onto the tip of the PCD electrode to construct the ultra micro glutamate sensor. The sensor shows stable response to glutamate and a response time within 12 s. The calibration range for glutamate measurement is 50–800 μM.     

Effects of uni-axial mechanical stress on IGBT characteristics

This paper describes the impacts of mechanical stress on vertical power devices. The stress dependence of the DC characteristics of trench insulated gate bipolar transistors (IGBTs) was measured. The experimental results could be reproduced by the device simulation, which included stress dependence models of the carrier mobility and the band gap. We found that the stress dependence of the on-state voltage mainly arose from the MOSFET portion of the IGBT. Using the device simulation, we estimated the effects of mechanical stress on the surge voltage and the saturation current, which give us the important information for designing a power module with higher ruggedness.